Trace element quantification at required detection limits can be very challenging. As one example, certain jurisdictions are moving to enforce environmental limits of 0.02-2 parts-per-million (ppm) for dangerous elements such as Cadmium in water streams, which is equivalent to 20-2000 parts-per-billion (ppb). The analytical performance goals placed on measurement technology to actually certify such low levels, often assessed using instrument level-of-detection (LOD), needs to be less than the regulated limit, possibly resulting in required LODs of less than one (1) ppb- or sub-ppb levels. The present invention is directed to reaching such limits using any type of measurement engine technology (X-RAY, ICP, AAS, MS, etc).
In one example of measurement technology, x-ray analysis is used across many test and monitoring applications such as environmental, consumer products, medical, pharmaceutical, and petroleum.
In one example of x-ray technology, x-ray fluorescence (XRF) is an analytical technique by which a substance is exposed to a beam of x-rays to determine, for example, the presence and concentrations of certain components. In XRF, at least some of the elemental constituents of the substance exposed to x-rays can absorb x-ray photons and produce characteristic secondary fluorescence. These secondary x-rays are characteristic of the elemental constituents in the substance. Upon appropriate detection and analysis these secondary x-rays can be used to characterize and/or quantify one or more of the elemental constituents in the sample.
Examples of XRF technology include U.S. Pat. Nos. 6,934,359 and 7,072,439, hereby incorporated by reference herein in their entirety and assigned to X-Ray Optical Systems, Inc., the assignee of the present invention. These patents disclose monochromatic wavelength dispersive x-ray fluorescence (MWD XRF) techniques and systems for the analysis of samples, e.g., trace level measurement of sulfur in petroleum products. U.S. Pat. No. 7,738,630, hereby incorporated by reference herein in its entirety and assigned to X-Ray Optical Systems, Inc., the assignee of the present invention, discloses monochromatic excitation, energy dispersive x-ray fluorescence (ME-EDXRF) techniques and systems for the analysis of samples, e.g., trace measurement of toxins in consumer products and other materials.
Many methods of analytical testing (including x-ray) take place off-line, i.e., using a bench-top, laboratory-type instrument to analyze a sample. The sample is removed from its environment (e.g., for fuel, from a refinery or transportation pipeline) and then deposited in a sample chamber; or into a windowed sample cell which is then deposited into a chamber. Off-line, bench-top instruments need not meet any unusual operational/pressure/environmental/size/weight/space/safety constraints, but merely need to provide the requisite measurement precision for a manually-placed sample. Moreover, off-line instruments can be easily maintained between measurements.
In contrast to off-line analysis, on-line analysis can provide “real-time” monitoring of sample composition at various points in a manufacturing process, a refinery, or in environmental stream handling. For example, all fuel products are subject to sulfur level compliance—requiring some variant of on-line monitoring during fuel refining and transportation in pipelines. On-line analysis, however, requires consideration of numerous operational issues not generally present in an off-line, laboratory setting. A fully automated sample handling system may be required—with little or no manual intervention or maintenance. Also, since fluids can be under varying pressure and flow in pipes or other channels, any sample handling system must account for pressure differentials.
What is required, therefore, to meet the challenges of such low detection levels, are improved techniques in sample handling, placement, x-ray excitation, and x-ray detection.